JP3664007B2 - Magnetic tape signal sound quality correction circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of audio equipment, and particularly relates to a sound quality correction technique at the time of recording from a magnetic tape to another recording medium.
[0002]
[Prior art]
Currently, in the audio industry, digital recording media such as mini-discs (MD) and CD-Rs (CD-Recordables) have emerged instead of magnetic tapes such as compact cassette tapes (hereinafter also referred to as C cassettes). I am doing. Therefore, there are not a few user needs to store audio signals recorded on magnetic tape, a legacy of the past, after correcting the sound quality on these new recording media.
[0003]
That is, the magnetic tape of analog recording has its magnetic force dropped due to aging, and the deterioration in the high sound range is remarkable. Also, tape wear due to contact resistance is a problem, which is the biggest cause of sound quality deterioration in the high sound range.
[0004]
Therefore, when dubbing is attempted after correcting the sound quality of the new recording medium, a graphic equalizer or a digital signal processor (DSP) has been used as a means until now.
[0005]
Sound quality correction by the former graphic equalizer is the most popular method for correcting deteriorated characteristics, but it can be said that it is a process of the same dimension as normal user control of sound quality. That is, the gain correction is performed by selecting the corresponding pole for the insufficient band (particularly the high frequency range).
[0006]
[Problems to be solved by the invention]
However, the biggest drawback of the high-frequency range correction by the graphic equalizer is that increasing the signal gain also amplifies the noise component and deteriorates the S / N ratio, which may result in a sound quality that is very difficult to hear. In particular, noise is worrisome in a quiet interlude portion where a signal of music such as a classic with a wide D range is not output. Typical characteristics are shown in FIG. 6 (the vertical axis represents gain (GAIN) and the horizontal axis represents frequency f). In FIG. 6, when the high-frequency correction on the high-frequency side of the signal characteristic is performed to increase the gain by 8 dB at 10 KHz, for example, the noise characteristic on the high-frequency range is also increased by about 8 dB at 10 KHz, and there is no sound. The noise is anxious in the state.
[0007]
In addition, sound quality correction means using a digital signal processor may be used for high-end audio equipment equipped with a DSP, but it is not suitable for deployment to popular priced products not equipped with a DSP. There's a problem.
[0008]
The present proposal provides an inexpensive magnetic tape signal correction circuit that eliminates these problems.
[0009]
[Means for Solving the Problems]
The present invention includes a sum / difference signal switching circuit 9 including a changeover switch SW1 for selecting either a sum signal or a difference signal of magnetic tape signals having two left and right channels (L / R), and the sum / difference signal switching circuit. A signal detection circuit 2 for detecting a sum signal or a difference signal of the magnetic tape signal selected in 9, and a filter circuit 3 for selecting only the high frequency side of the sum signal or the difference signal detected by the signal detection circuit 2; Further, the detection circuit 4 for detecting the signal in the high frequency range side and a selection switch SW2 for a plurality of time constant circuits are provided to control the high frequency range detection signal detected by the detection circuit 4, thereby correcting the high frequency range emphasis. The time constant switching circuit 8 for switching the level, and the high frequency side gain of the left and right two-channel magnetic tape signals only when the high sound range detection signal S through the time constant switching circuit 8 exceeds a predetermined level. Above each To solve the above problems by providing emphasizing the high frequency range correcting circuits 5 and 6, a magnetic tape signal sound quality correction circuit 20, characterized in that it comprises a Te.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is a block diagram of a magnetic tape signal sound quality correction circuit having a basic configuration according to the present invention, and FIG. 2 is a block diagram of a more preferable magnetic tape signal sound quality correction circuit according to the present invention. FIG. 3 is a circuit diagram embodying the block diagram of FIG.
[0012]
The greatest feature of the magnetic tape signal sound quality correction circuit according to the present invention is that real-time reproduction / recording is possible by correcting only the high sound range side when there is a signal without deteriorating the S / N ratio so much. .
[0013]
That is, in FIG. 1, the magnetic tape signal sound quality correction circuit 10 outputs a sum signal (L + R) or a difference signal (LR) of a magnetic tape signal having two left and right channels (Lch / Rch) from the compact cassette block 1. A signal detection circuit 2 to be detected, a filter circuit 3 for selecting only the high frequency side of the sum signal (L + R) or difference signal (LR) detected by the signal detection circuit 2, and the selected high frequency signal And a high-frequency-side gain of the left and right two-channel magnetic tape signals (L / R) are increased and emphasized only when the detected high-frequency range detection signal S exceeds a predetermined level. The corrected output is connected to the next stage of the reproduction system and the recorder 7 (MD or CD-R recorder). It is done. The filter circuit 3 may be a high-pass filter, but preferably, as a band-pass filter (BPF), for example, only a high-frequency signal from 4 KHz to around 16 KHz is sent to the detection circuit 4.
[0014]
Whether the sum signal (L + R) or the difference signal (LR) of the magnetic tape signal is detected is arbitrary, but a stereo signal has a slight difference in audibility between the two, and in general, a sum signal is not obtained. This is a harder sensation, and in the case of a difference signal, the sense of stereo is high with a natural sensation. In the case of a monaural signal, a difference signal does not produce a signal, so a sum signal is preferable because the high-frequency correction of the present invention is possible.
[0015]
Based on the above consideration, the signal detection circuit 2 can be arbitrarily selected by the user without fixing whether the sum signal (L + R) or the difference signal (LR) of the magnetic tape signal is detected. Is preferable in terms of answering the tastes and needs of various users.
[0016]
However, in the more preferable magnetic tape signal sound quality correction circuit 20 shown in FIG. 2, in addition to the above-described configuration, the sum / difference signal switching circuit 9 for selecting either the sum signal or the difference signal of the magnetic tape signal is detected. It is added to the input side of the circuit 2. This sum / difference signal switching circuit 9 performs signal detection with the L / R sum signal (L + R) of the left and right channels when the signal is monaural or close to monaural, and each L / R alone or high frequency Allows correction. On the other hand, when the signal is stereo, differential signal detection is performed to remove the sense of incongruity and to expand the sound field to widen the L / R separation. Each detection method can be controlled by the changeover switch SW1, and the user can freely select matching with music.
[0017]
Next, the basic configuration of FIG. 1 is based on the fundamental principle of emphasizing the high frequency range according to a predetermined level of the sum / difference signal of the magnetic tape signal. There are complaints that can only be done. That is, it is preferable that the correction level of high-frequency range emphasis (responsiveness of the effect of high-frequency range correction) can be selected so as to have a user-preferred tone.
[0018]
However, in addition to the basic configuration shown in FIG. 1, the high-frequency correction circuit 5 includes a high-frequency range detection signal S detected by the detection circuit 4 via a time constant switching circuit 8 having a plurality of time constant circuit selection switches SW2. The magnetic tape signal sound quality correction circuit 20 shown in FIG.
[0019]
The selection switch SW2 constant switching circuit 8 when performing switching of the correction level, the correction level of the high frequency range emphasis as yourself is changed selectively by controlling the high-frequency detection signal S, diverse music Application to genres (improves response to differences in rhythm, etc.) is possible.
[0020]
The actual circuit for realizing the magnetic tape signal sound quality correction circuit 20 of FIG. 2 to which the sum / difference signal switching circuit 9 and the time constant switching circuit 8 for switching the correction level are added will be described below with reference to FIGS. Based on the explanation.
[0021]
The L / R audio signal output from the compact cassette block 1 is input to the operational amplifier of the signal detection circuit 2 via the changeover switch SW1 of the sum / difference signal changeover circuit 9. By switching the switch SW1, the operational amplifier can select differential amplification or addition amplification.
[0022]
Thereafter, a desired frequency band is selected by the BPF configured by the secondary HPF and the primary LPF as the filter circuit 3. Here the capacitor C4, C5 22 0 pF, the resistors R5 15K, the resistance R6 220KΩ, the cutoff frequency of the secondary HPF by a resistor R8 and 8.2KΩ becomes FL = 10170Hz. On the other hand, if the resistor R9 is 3.3 KΩ and the capacitor C7 is 56 0 pF, FH is 86039 Hz. The band constituted by both is BPF = 10170 to 86038 Hz.
[0023]
The detection circuit 4 is composed of a double voltage rectifier and smoothing circuits by diodes D1 to D3. The rectified output is connected to the time constant switching circuit 8 as a high sound range detection signal S via a buffer circuit composed of transistors TR1 and TR2 for stabilization. The time constant switching circuit 8 can determine the integral value of the detection output per time by switching the time constant circuit determined by the capacitor C11 and the resistor R15 and the time constant circuit to which the resistor R16 is added by the selection SW2. That is, it is possible to control the level of high-frequency emphasis at the next stage. In this embodiment, two-stage switching is used, but it is needless to say that multistage switching beyond that is possible.
[0024]
The high frequency correction circuits 5 and 6 are provided in each of the L / R. The high-frequency correction circuit 5 (the same applies to the high-frequency correction circuit 6) is a primary filter composed of a capacitor C12, a resistor R18, a resistor R19, and an FET1, and its operation depends on the detection circuit 4 in the previous stage. ON / OFF is controlled by a high sound range detection signal S connected to the gates of FET1 and FET2. In FIG. 4 showing the principle and characteristic diagram, when the FET 1 is turned on, the characteristic becomes the ON mode of FIG. Conversely, in the OFF mode, the primary filter does not operate and the non-emphasis mode is set (OFF mode).
[0025]
For example, the high frequency emphasis band where the resistor R18 is 10 KΩ, the capacitor C12 is 0.0039 μF, and the resistor R19 is 6.8 KΩ,
f1 = 1 / 2π · C12 · R18 = 4077Hz
f2 = R18 · R19 / 2π · C12 · (R18 + R19) = 165179Hz
The gain increases in the range given by (approximately 8 dB at 10 KHz).
[0026]
The high frequency correction circuits 5 and 6 perform active control by performing the above operation corresponding to the actual music source level, and high frequency emphasis is performed when there is almost no high frequency signal (in the OFF mode). No increase in noise is avoided.
[0027]
The characteristic diagram of FIG. 5 shows the accumulated noise distribution characteristics when the high frequency range emphasis correction circuit is operated (EFFECT ON) and when it is not operated (EFFECT OFF) when the actual music source is played for 1 minute. FIG. From the figure, it can be seen that the increase in the accumulated noise is slightly suppressed by 2 dB when the operation is performed and when the operation is not performed. In other words, since the high frequency range correction is limited only to signal detection, the S / N ratio does not deteriorate and the high frequency range audio is output (normally, the time ratio is small). The noise increase caused by the masking effect is not noticeable.
[0028]
In addition, the quality of the compact cassette block 1 as an audio device is not defined. The recorder 7 is not limited, but at the present time, an MD recorder, a CD-R recorder, or the like can be considered as a digital recorder.
[0029]
Further, there is no problem even if the high frequency range correction circuits 5 and 6 are provided in each of the reproduction system / recording system.
[0030]
【The invention's effect】
As described above, the magnetic tape signal sound quality correction circuit according to the present invention has the following excellent effects.
(1) It is possible to correct the high frequency range where the magnetic recording tape, which is also a past asset, has deteriorated without deteriorating the S / N, and to upgrade the sound.
(2) The sound of the magnetic tape whose treble range has been corrected can be stored in another recording medium simultaneously with reproduction.
(3) The user can arbitrarily select emphasis of high-frequency range correction with the selection switch of the sum / difference signal detection circuit according to preference.
(4) The emphasis level of high-frequency range correction can be selected by the changeover switch of the correction level changeover circuit, and the user preference can be applied to various music genres.
[Brief description of the drawings]
FIG. 1 is a block diagram of a magnetic tape signal sound quality correction circuit having a basic configuration according to the present invention.
FIG. 2 is a block diagram of a more preferred magnetic tape signal sound quality correction circuit according to the present invention.
3 is a circuit diagram example that embodies the block diagram of FIG. 2;
FIG. 4 is a diagram showing the principle and characteristic diagram of a high-frequency correction circuit.
FIG. 5 is a diagram showing an accumulated noise distribution characteristic when an actual music source is played for one minute.
FIG. 6 is a characteristic diagram of a typical audio signal and noise when high-frequency range correction is performed by a graphic equalizer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Compact cassette block 2 Signal detection circuit 3 Filter circuit 4 Detection circuit 5, 6 High region correction circuit 7 Recorder 8 Time constant switching circuit 9 Sum / difference signal switching circuit 10, 20 Magnetic tape signal sound quality correction circuit FL Low frequency side cut off Frequency FH High-frequency cutoff frequency S High-frequency detection signal SW1, SW2 selector switch

Claims (1)

A sum / difference signal switching circuit having a selector switch for selecting either a sum signal or a difference signal of magnetic tape signals having two left and right channels; and a sum of the magnetic tape signals selected by the sum / difference signal switching circuit A signal detection circuit for detecting a signal or a difference signal, a filter circuit for selecting only the high frequency side of the sum signal or difference signal detected by the signal detection circuit, a detection circuit for detecting the signal on the high frequency side, and a plurality of A time constant switching circuit for switching a correction level for emphasizing the high range by controlling a high range detection signal detected by the detection circuit, and a time constant switching circuit including the time constant circuit selection switch. And a high-frequency range correction circuit that increases and emphasizes the high-frequency gain of the left and right two-channel magnetic tape signals only when the detected high-frequency range detection signal exceeds a predetermined level. Magnetic tape signal sound quality correction circuit.

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